1. Field of the Invention
The present invention relates to corrugated paper board manufacture and, more specifically, to corrugator belts for the corrugator machines used to manufacture that variety of paper board.
2. Description of the Prior Art
The manufacture of corrugated paper board, or box board, on corrugator machines is well-known in the art. On such machines, corrugator belts pull a web of corrugated board first through a heating zone, where an adhesive used to bond layers of the web together is dried or cured, and then through a cooling zone. Frictional forces between the corrugator belt, specifically the so-called board side thereof, and the web are primarily responsible for pulling the latter through the machine.
The corrugator belts employed to pull the web of corrugated board through the corrugator machine should be strong and durable, and should have good dimensional stability under the conditions of tension and high temperature encountered on the machine. The belts must also be comparatively flexible in the longitudinal, or machine, direction, while having sufficient rigidity in the cross-machine direction to facilitate the guiding of the belts along their endless paths. Traditionally, it has also been desirable for the belts to have sufficient porosity for vapor to pass freely therethrough, while being sufficiently incompatible with moisture to avoid the adsorption of condensed vapor which might otherwise rewet the surfaces of the corrugated product.
As implied in the preceding paragraph, a corrugator belt takes the form of an endless loop when installed on a corrugator machine. In such form, the corrugator belt has a board-side, as previously mentioned, and a back side, which is on the inside of the endless loop. Frictional forces between the surface of the back side and the drive rolls of the corrugator machine move the corrugator belt, and frictional forces between the surface of the board side and the web of corrugated board pull the web through the machine.
Corrugator belts are generally flat-woven, multi-layered fabrics, each of which is trimmed in the lengthwise and widthwise directions to a length and width appropriate for the corrugator machine on which it is to be installed. The ends of the fabrics are provided with seaming means, so that they may be joined to one another with a lacing cable when the corrugator belt is being installed on a corrugator machine.
In a typical corrugator machine, the heating zone comprises a series of hot plates across which the web of corrugated board is pulled by the corrugator belt. A plurality of weighted rollers within the endless loop formed by the corrugator belt press the corrugator belt toward the hot plates, so that the corrugator belt may pull the web across the hot plates under a selected amount of pressure. The weighted rollers ensure that the web will be firmly pressed against the hot plates, and that frictional forces between the corrugator belt and the web will be sufficiently large for the belt to pull the web.
In a new generation of corrugator machines, however, weighted rollers are being eliminated in favor of air impingement or air bearings, in which a high-velocity flow of air directed against the back side of the corrugator belt toward the hot plates forces the belt towards the hot plates. Corrugator belts currently available have permeabilities in the range from 3 to 20 cubic feet of air per square foot per minute under 0.5 inch water pressure. While this is quite low, it has proven to be large enough to allow enough air from the air bearings to pass through the corrugator belt to lift the belt from the web of corrugated board. This leads to slippage between belt and web, and to poor contact between web and hot plates, the latter of which ultimately leads to poor, non-uniform bonding in the laminated corrugated board product.
Clearly, a corrugator machine of this new type requires a totally sealed, impermeable corrugator belt. The present invention is such a belt.